Hydrogenation of substrate and products manufactured according to the process

ABSTRACT

A typical traditional reactor for hydrogenation consists of a tank filled with a liquid and a gas and a small particle catalyst. The reaction is carried out at high pressures and high temperatures. Lack of gas on the catalyst surface limits the velocity of reaction. Much work has been done to increase the quantity of gas on the catalyst. It has not been possible to solve this problem effectively with the techniques of today. According to the invention an extra solvent is added to the reaction mixture. By bringing the whole mixture (solvent, substrate, hydrogen and reaction products) to super-critical or near-critical state, a substantially homogeneous mixture can be obtained. By this method it is possible to control the concentration of gas on the catalyst to the desired level. The velocity of reaction is thereby increased considerably. The hydrogenation reactions principally involved comprise hydrogenation of carbon-carbon double bonds (C═C) in lipids; hydrogenation of COOR to C--OH and HO--R to produce fatty alcohols; and direct hydrogenation of oxygen to hydrogen peroxide.

This application is a 371 of PCT/SE95/00824 filed Jul. 3, 1995.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a process for the hydro-genation of asubstrate, where hydrogen gas is mixed with the substrate in thepresence of a catalyst and the reaction is carried out at certainreaction conditions of pressure, time and temperature. The hydrogenationreactions are mainly related to the hydrogenation of carbon-carbondouble bonds (C═C) in lipids;

hydrogenation of COOR to C--OH and HO--R for the manufacturing of fattyalcohols; and the direct hydrogenation of oxygen to hydrogen peroxide.

BACKGROUND OF INVENTION

C═C in lipids.

The annual production of vegetable oils is about 90.million tons (Mielke1992), of which about 20% are hardened (hydrogenated). Furthermore,about 2 million tons of marine oils are hydrogenated yearly. Theproduction is spread over the whole industrialized world. Through thehydrogenation, hydrogen is added to the double bonds of the unsaturatedfatty acids. The largest part of the oils is only partly hydrogenated.The desired conditions of melting and the desired consistency of thefats are thereby obtained, which are of importance for the production ofmargarine and shortening. The tendency to oxidation is reduced by thehydrogenation, and the stability of the fats is increased at the sametime (Swern 1982).

In the future, the lipids may be modified by methods belonging to biotechnology, especially gene technology, but hydrogenation will certainlyremain.

A problem with the hydrogenation processes of today is, that new fattyacids are produced which to a great extent do not exist in the nature.They are often called trans fatty acids, but the double bonds changeposition as well as form (cis-trans) during the hydrogenation (Allen1956, Allen 1986).

As a rule, trans fatty acids are desired from a technical and functionalpoint of view (Swern 1982), but regarding health, their role is becomingmore and more questionable (Wahle & James 1993).

A typical state of the art reactor for hydrogenation is a large tank (5to 20 m³) filled with oil and hydrogen gas plus a catalyst in the formof fine particles (nickel in powdery form). The reaction is carried outat a low pressure, just above atmospheric (0.5 to 5 bar), and hightemperatures (130 to 210° C.). The hydrogen gas is thoroughly mixed intothe oil, as this step restricts the reaction rate (Grau et al., 1988).

If the pressure of hydrogen gas is increased from 3 to 50 bar when soyaoil is partially hydrogenated (iodine number at the start=135, at theend=70), the content of trans is reduced from 40 to 15%. The positionisomerization is also reduced to a corresponding level (Hsu et al.,1989). These results are of no commercial interest, as these conditionsenforce a replacement of the low pressure autoclaves by high pressureautoclaves.

According to the "half hydrogenation" theory, the concentration ofactivated H-atoms on the catalyst surface determines the number ofdouble bonds being hydrogenated and deactivated without beinghydrogenated respectively. A lack of activated H-atoms causes a trans-and position-isomerization (Allen 1956, Allen 1986). A lack of activated

H-atoms can be the consequence of low solubility of H₂ in the oil, or ofa bad catalyst (poisoned or inadequately produced). Thus, the "halfhydrogenation" theory corresponds very well to the empirical results(Allen 1956; Allen 1986; Hsu et al., 1989).

It is possible to deodorize and hydrogenate an oil in the presence ofCO₂ and hydrogen (Zosel 1976). Zosel describes in detail how to use CO₂in order to deodorize the oil. However, it must be emphasized that Zoseldoes not give any hint, that CO₂ should have an influence on thehydrogenation process. Furthermore, Zosel does not touch on thecis/trans problem.

In the experiments of Zosel, the catalyst is surrounded by a liquidphase during the entire process. Zosel does not disclose thecomposition, but in the light of the other data, we estimate that theliquid phase consists of oil (about 95%), CO₂ (about 5%) and hydrogen(about 0.03%). This phase is far away from a supercritical condition. Asa consequence, the velocity of reaction is limited by the concentrationof hydrogen on the catalyst surface. The same applies to all traditionalhydrogenation reactions where the catalyst is in the liquid phase aswell. The velocity of hydrogenation in the experiments of Zosel is about100 kg/m³ h, i.e. somewhat lower than in traditional hydrogenizingreactors.

FATTY ALCOHOLS.

Fatty alcohols and their derivatives are used in shampoo, detergentcompositions and cosmetic preparations etc. The annual production isabout 1 million tons. About 60% is based on petrochemicals, and about40% is derived from natural fats and oils. The raw material for shortchain fatty alcohols, C₁₂ -C₁₄, is coco-nut oil and palm kern oil,whereas C₁₆ -C₁₈ comes from tallow, palm oil or palm stearin (Kreutzer1984, Ong et al., 1989).

It is theoretically possible to hydrogenate triglycerides, fatty acidsand methylesters to fatty alcohols. A direct hydrogenation oftriglycerides has not been developed commercially, because the glycerolwill be hydrogenated as well and thus lost. A direct hydrogenation offatty acids requires corrosion resistant materials and a catalystresistant to acids (Kreutzer 1984). Lurgi has developed a hydrogenationprocess (the slurry process), where fatty acids are introduced and arequickly esterified with a fatty alcohol to a wax ester, and then the waxester is hydrogenated (copper chromite, 285° C., 300 bar)(Buchhold 1983,Voeste Buchhold 1984, Lurgi 1994).

Most plants for the production of natural fatty alcohols are based onmethyl esters as raw material. Saturated fatty alcohols are produced ata temperature of about 210° C. and a pressure of 300 bar using copperchromite as catalyst in a fixed bed reactor. Other catalysts as coppercarbonate, nickel or copper and chromic oxide will also function(Mahadevan 1978, Monick 1979, Lurgi 1994). Unsaturated fatty alcoholsare produced at about 300° C. and 300 bar, normally using zinc chromiteas catalyst. There are also other catalysts which selectivelyhydrogenate the group COOR, leaving the C═C unimpaired (Klonowski etal., 1970; Kreutzer 1984).

The reaction is limited by the solubility of hydrogen in the liquid(Hoffman Ruthhardt 1993).

Davy Process Technology markets a gas phase process where methyl estersare hydrogenated to fatty alcohols (40 bar, 200 to 250° C., catalystwithout chromium) (Hiles 1994).

A lot of work has been done to develop catalysts functioning with lessenergy (lower temperature, lower pressure). Another object has been todevelop methods for a direct hydrogenation of triglycerides to fattyalcohols without a simultaneous hydrogenation of the glycerol (HoffmanRuthhardt 1993).

HYDROGEN PEROXIDE.

Hydrogen peroxide is used in large quantities for bleaching, cleaning,as a disinfectant and as a raw material in industrial processes etc.Earlier, hydrogen peroxide was derived by an electrolytic process. Now,oxidation of substituted hydroquinone or 2-propanol is most widely used.

There are a lot of patents concerned with direct synthesis of hydrogenperoxide from oxygen and hydrogen. The reaction medium can be acidicorganic solvents or water with organic solvents using noble metals, mostoften palladium, as catalyst (EP-B-0049806; EP-B-0117306; U.S. Pat. No.4,336,239; EP-B-0049809).

It is preferred that the reaction medium is free from organicconstituents because of problems with purification. Several patents useacidic water as the reaction medium (pH=1-2) with addition of halides,especially bromide and chloride (<1 mM) and with noble metals ormixtures of noble metals as catalysts (EP-A-0132294; EP-A-0274830; U.S.Pat. No. 4,393,038; DE-B-2655920; DE 4127918 A1).

The velocities of reaction which are disclosed are about 1 kg/m³ h, andthe selectivity (mol hydrogen peroxide/mol hydrogen reacted) is about75% (DE 4127918 A1).

According to theory, one can expect to obtain- high selectivity withhigh concentrations of oxygen and hydrogen on the catalyst surface(Olivera et al., 1994).

The object of the present invention is to obtain a very effectiveprocess for partial or complete hydrogenation of the substratesmentioned above.

According to the invention, this problem has been solved by mixing thesubstrate, hydrogen gas and solvent, and by bringing the whole mixtureinto a super-critical or near-critical state. This substantiallyhomogeneous super-critical or near-critical solution is led over thecatalyst, whereby the reaction products formed, i.e. the hydrogenatedsubstrates, will also be a part of the substantially homogeneoussupercritical or near-critical solution.

The solvent can be a saturated hydrocarbon or an unsaturated hydrocarbonwhich on hydrogenation gives a saturated hydrocarbon, e.g. ethane,ethene, propane, propene, butane, butene, or CO₂, dimethyl ether,"freons", N₂ O, N₂, NH₃, or mixtures thereof.

Propane is a suitable solvent for many lipids. CO₂ is a suitable solventfor hydrogen peroxide and water.

The catalyst will be selected according to the reaction which is to becarried out. For a partial or complete hydrogenation of only C═C bonds,preferably a noble metal or nickel will be selected. For a selectivehydrogenation of COOR to C-- OH and HO--R, the catalyst would preferablybe a zinc salt, e.g. zinc chromite. For a simultaneous hydrogenation ofCOOR to C--OH and HO--R and a hydrogenation of C═C, the preferredcatalyst would be copper chromite, another salt of copper or copper freefrom chrome. For a partial hydrogenation of oxygen to hydrogen peroxide,the preferred catalyst would be a noble metal.

According to the invention, the concentration of hydrogen on thecatalyst surface can be controlled to very high levels. The proportionof trans fatty acids in partially hydrogenated fatty products will bemuch lower according to the invention than by using conventionalprocesses, where the product has been hydrogenated to the same levelusing the same catalyst. The hydrogenated products will preferablycontain less than 10% trans fatty acids.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the percentage of trans fatty acids as afunction of the degree of hydrogenation according to a traditionaltechnique and according to the invention.

FIG. 2 is a flow sheet for a process according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In a great number of hydrogenation processes, hydrogen gas is mixed witha liquid substrate and a fixed catalyst, e.g. in the hydrogenation oflipids. In certain cases the substrate can be a gas and the product aliquid, e.g. hydrogenation of oxygen to hydrogen peroxide and water. Inboth these cases, the velocity of reaction is limited by theconcentration of gas on the catalyst surface. The reason is thetransport resistances of the gas: between the gas phase and the liquidphase; through the liquid phase; and between the liquid phase and thecatalyst.

In accordance with the present invention a solvent is added whichcompletely dissolves the gas as well as the liquid, resulting in asubstantially homogeneous mixture of hydrogen, substrate, product andsolvent. This is possible, if the whole mixture is in a super-criticalor near-critical state. The defition substantially homogeneous means,that the principal part of the gas is in the continuous phase whichcovers the catalyst surface. One method to confirm this is to observethe velocity of reaction, which increases dramatically when thecontinuous phase that covers the catalyst surface is substantiallyhomogeneous.

VELOCITY OF REACTION.

According to the invention, the following transport resistances of thegas are reduced substantially: gas phase/liquid phase; through theliquid phase; and liquid phase/catalyst. The velocity of reactionthereby increases to a very high degree; from about 10 to about 1000times. The consequence of this is that continuous reactors will bepreferred compared to the batch reactors of to-day. The selectivity isalso influenced to a very high degree.

SOLVENT.

In order to bring the whole mixture (hydrogen, substrate product andsolvent) to super critical or near-critical state at appropriatepressures and temperatures, the solvent must dissolve substrate andproduct as much as possible.

Glycerides, fatty acids and many derivatives of fatty acids arecompletely miscible with super-critical propane (Peter et al., 1993).Propane can be used in any proportions together with food according toEU-regulations (Sanders 1993; EC 1984). Thus, propane is a very adequatesolvent in reactions with lipids.

Water dissolves to a certain extent in CO₂ (King et al., 1992). Hydrogenperoxide dissolves more easily than water in CO₂. Thus, CO₂ is anappropriate solvent for direct synthesis of hydrogen peroxide. (For athorough description of super-critical technology, see McHugh Krukonis1986; Dohrn 1994).

CATALYSTS.

The catalysts which are used today in traditional processes can inprinciple also be used in super-critical processes. The catalyst mayhowever be modified to optimize selectivity, velocity of reaction,length of life, filtering properties and pressure-drop.

QUALITY OF PRODUCT.

The invention enables new possibilities to control the hydrogenconcentration at the catalyst. The velocity of reaction increasessubstantially. The selectivity can also be influenced in certainprocesses. By partial hydrogenation of edible oils, the content of transfatty acids is of importance for the quality (see background ofinvention).

FIG. 1 illustrates in principle how the proportion of trans fatty acidschanges during hydrogenation with two different catalysts, one catalystaccording to a traditional technique and another according to the newsuper-critical technique. The new supercritical technique makes itpossible to reduce the content of trans fatty acids in comparison withthe traditional technique using the same catalyst and the same degree ofhydrogenation. However, using different catalysts, the difference may beless.

In FIG. 1, "trad" means traditional process; "sf" means process withsuper critical fluid; and "cat" means catalyst.

CONDITIONS OF REACTION.

C═C in lipids.

I. Partial hydrogenation.

At partial hydrogenation, the reaction is interrupted at a certainiodine number, e.g. 60. The substrate, e.g. vegetable, animal or marineoil, and hydrogen are dissolved in a solvent, e.g. propane. The mixtureis brought to a supercritical or a near-critical state. Thesubstantially homogeneous mixture is brought into contact with acatalyst, e.g. palladium. The content of trans fatty acids in the finalproduct is less than 10%. The optimal reaction condition may occure overa wide experimental range and this range can be described as follows:

    ______________________________________                in general  preferably    ______________________________________    temperature   0-250° C.                                20-200° C.    pressure      10-350 bar    20-200 bar    time of reaction                  0*-10 min     1 μsec-1 min    solvent       30-99.9 wt %  40-99 wt %    ______________________________________

The solvent must dissolve the substrates at the concentrations used. Thesolvent can be ethane, ethene, propane, propene, butane, butene, CO₂,dimethyl ether, "freons", N₂ O, N₂, NH₃ or mixtures of these gases.Preferred are propane, propene, butane, butene and dimethyl ether. Mostpreferred is propane.

    ______________________________________    concentration of H.sub.2                   0*-3 wt %    0.001-1 wt %    concentr.substrate                   0.1-70 wt %  1-60 wt %    ______________________________________

-type of substrate:

C═C in general. Glycerides are preferred (mono-, di-, triglycerides,galactolipids, phospholipids), also fatty acids or their derivatives(e.g. methyl- and ethyl-esters).

-catalysts

noble metals: Pd, Pt, Os, . . . but also Ni.

(0* means very low values, below the lowest one under "preferably").

II. Complete hydrogenation.

At complete hydrogenation, all double bonds are hydrogenated and theiodine number is therefore near zero. The substrate, e.g. vegetable,animal or marine oil, and hydrogen are dissolved in a solvent, e.g.propane. The mixture is brought to a supercritical or near-criticalcondition, and the substantially homogeneous mixture is brought intocontact with a catalyst, e.g. palladium.

The optimal conditions of reaction are wide and can be described in asimilar way as for partial hydrogenation; the temperature is, however,somewhat higher than for partial hydrogenation (T is probably higherthan T_(crit)).

FATTY ALCOHOLS.

The substrate, e.g. the triglyceride, the fatty acid or its derivative,and hydrogen are mixed together with a solvent, e.g. propane. Themixture is brought to a super-critical or a near-critical state, and thesubstantially homogeneous mixture is brought into contact with acatalyst. Different groups can be hydrogenated depending on the catalystused (see below under "-catalyst").

The optimal reaction condition may occure over a wide experimental rangeand this range can be described as follows:

    ______________________________________                in general  preferably    ______________________________________    temperature   20-300° C.                                40-300° C.    pressure      10-350 bar    20-200 bar    time of reaction                  0*-10 min     1 μsec-1 min    solvent       30-99.9 wt %  40-99 wt %    ______________________________________

The solvent must dissolve the substrates at the concentrations used. Thesolvent can be ethane, ethene, propane, propene, butane, butene, CO₂,dimethyl ether, "freons", N₂ O, N₂, NH₃ or mixtures of these gases.Preferred are propane, propene, butane, butene, and dimethyl ether.Sometimes, it can be advantageous to use an entrainer. Most preferred ispure propane.

    ______________________________________    concentration H.sub.2                   0*-3 wt %    0.001-1 wt %    concentr.substr.                   0.1-70 wt %  1-60 wt %    ______________________________________

-type of substrate:

COOR in general. Preferred are fatty acids and their derivatives (e.g.methyl-ethyl- or wax esters), and also mono- di-, and tri-glycerides,but also galactolipids and phospholipids.

-catalyst:

a) selective hydrogenation of COOR, but not C═C or C--OH, e.g. zincchromite or any other salt of zinc.

b ) hydrogenation of both COOR and C═C, but not C--OH, e.g. copperchromite, copper free from chrome or any other salt of copper.

(0* means very low values, less than the lowest one under "preferably").

An example of suitable values at optimal conditions is:

substrate 10 wt %, propane about 90 wt %, hydrogen 0.2 wt %; the mixtureis brought into contact with a bed of catalyst at 250° C. and 150 bar,and has an average contact time of 30 sec.

HYDROGEN PEROXIDE.

Oxygen and hydrogen are mixed in a solvent, e.g. CO₂. The mixture isbrought to a super-critical or near-critical state, and thesubstantially homogeneous mixture is brought in contact with a catalyst.The solvent dissolves the reaction products, hydrogen peroxide andwater. Thus, a substantially homogeneous mixture is maintained in thereactor.

The optimal reaction condition may occure over a wide experimental rangeand this range can be described as follows:

    ______________________________________                in general  preferably    ______________________________________    temperature   10-200° C.                                20-10 0° C.    pressure      10-350 bar    30-300 bar    time of reaction                  0*-10 min     1 μsec-1 min    solvent       10-99.9 wt %  60-99 wt %    ______________________________________

The solvent must dissolve water and hydrogen peroxide at theconcentrations used. The solvent can be CO₂, N₂, NH₃, or mixtures ofthese gases. It may also be advantageous to use an entrainer. Pure CO₂is probably the most suitable solvent.

    ______________________________________    concentration H.sub.2                   0*-10 wt %   0.1-3 wt %    concentration O.sub.2                   0.1-80 wt %  1-30 wt %    ______________________________________

-catalyst:

noble metals, e.g. Pd or mixtures of noble metals, e.g. Pd+Au

-reaction aids:

halides, e.g. bromides or chlorides; these can be added in thepreparation of the catalyst

(0* means very low values, less than the lowest under Y preferably")

The risk of explosion during some of the processing steps must be warnedagainst.

Suitable proportions of the added constituents can be exemplified by:oxygen 3 wt %, hydrogen 0.1 wt % and CO₂ 96.9 wt %. The mixture isbrought into contact with a catalyst of palladium at 35° C. and 200 bar;the average contact time is 0.1 sec.

EQUIPMENT AND ANALYTICAL METHODS

Equipment

A flow sheet for the continuous reactor used, is illustrated in FIG. 2.In this figure "M" is a mixer, "Temp." a temperature controller, "A" asampling device for analyses, "P" a pressure reduction valve, "Sep" avessel for separation of gas/liquids and "F" a gas flow-meter. At roomtemperature a condensed gas, a non-condensable gas and a liquid weremixed according to the principles used by Pickel in a "SupercriticalFluid Chromatography" application (Pickel 1991). Pickel mixed CO2nitrogen and a liquid entrainer. We mixed propane (l), hydrogen (g) andlipids (see M in FIG. 2). The same equipment can be used for thehydrogen peroxide experiments but in this case one add: CO₂ (l);oxygen+hydrogen (g); reaction aids (l).

The mixture was heated to the desired reaction temperature and wasbrought into an HPLC tube filled with a catalyst powder (see Temp andReactor in FIG. 2).

After the reactor samples were collected from the high pressure sectionusing an HPLC valve (see A in FIG. 2 and Harrod et al 1994).

The pressure was reduced to atmospheric pressure and lipids and gaseswere separated (see P and Sep in FIG. 2). Then the gas flow was measured(see F in FIG. 2) The gasflow was controlled by the pressure-reductionvalve (P in FIG. 2).

Analysis

The product quality was analysed using silver-ion-HPLC and gradientelution (Elfman Harrod 1995). This method is developed from an isocraticmethod (Adolf 1994). The kind (cis/trans) and the amount of the fattyacid methyl esters (FAME) was determine. From these data the iodinevalue (IV) was calculated.

The density was calculated from the Peng-Robinsson equation of state(Dohrn 1994).

EXAMPLES Example 1

Partial hydrogenation of methylesters from rapeseed oil using apalladium catalyst.

Composition and amound of the inlet flow to the reactor:

    ______________________________________           mole %     weight % mg/min    ______________________________________    propane  99.92        99.7     3700    hydrogen 0.04         0.002    0.07    FAME     0.04         0.26     10    ______________________________________

Reaction conditions:

    ______________________________________    catalyst      5% Pd on char coal (E 101 O/D 5%                  Degussa AG)    reactor volume                  0.007 ml    reaction time 40 ms    temperature   50° C.    pressure      120 bar    ______________________________________

productivity and product quality:

    ______________________________________    productivity      80 000 kg FAME/m.sup.3 h    Iodine-value      reactor inlet = 110                      reactor outlet = 50    FAME with trans   10% of all FAME    ______________________________________

Comments

This example shows that a very high productivity (80 000 kg FAME/m³ h)and a low content of trans-fatty acids (10%) can be attained atnear-critical conditions. The results above is only an example. We donot claim that it is the optimal conditions for the process.

Others (Berben et al 1995) has minimized the trans-fatty acid contentusing the conventional technique. The productivity became much lower(700 kg triglycerides /m³ h) and the content of the trans-fatty acidsbecame much higher (34%).

Example 2

Complete hydrogenation of methylesters from rapseed oil using aPalladium catalyst.

Composition and amount of the inlet flow to the reactor:

    ______________________________________           mole %     weight % mg/min    ______________________________________    propane  96.27        95.7     1840    hydrogen 3.1          0.14     2.7    FAME     0.63         4.16     80    ______________________________________

Reaction conditions:

    ______________________________________    catalyst      5% Pd on char coal (E101 O/D 5                  Degussa AG)    reactor volume                  0.007 ml    reaction time 80 ms    temperature   90° C.    pressure      70 bar    ______________________________________

productivity and product quality:

    ______________________________________    productivity      700 000 kg FAME/m.sup.3 h    Iodine-value      reactor inlet = 110                      reactor outlet <1    FAME with trans   <0.1% of all FAME    ______________________________________

Comments

This example shows that a tremendous productivity (700 000 kg FAME/m³ h)can be attained at near-critical conditions. The results above is onlyan example. We do not claim that it is the optimal conditions for theprocess.

Example 3

Complete hydrogenation of methylesters from rapeseed oil using a nickelcatalyst.

Composition and amount of the inlet flow to the reactor:

    ______________________________________           mole %     weight % mg/min    ______________________________________    propane  99.49        99.13    1500    hydrogen 0.38         0.017    0.25    FAME     0.13         0.85     13    ______________________________________

Reaction conditions:

    ______________________________________    catalyst        Nickel (Ni-5256 P, Engelhard)    reactor volume  0.009 ml    reaction time   65 ms    temperature     190° C.    pressure        155 bar    ______________________________________

productivity and product quality:

    ______________________________________    productivity      90 000 kg FAME/m.sup.3 h    Iodine-value      reactor inlet = 110                      reactor outlet <1    FAME with trans   <0.1% of all FAME    ______________________________________

Comments

This example shows that a very high productivity (90 000 kg FAME/m³ h)can be attained using a nickel catalyst at super-critical conditions.The results above is only an example. We do not claim that it is theoptimal conditions for the process.

Example 4

Complete hydrogenation of triglycerides using a palladium catalyst.

Composition and amount of the inlet flow to the reactor:

    ______________________________________            mole %     weight % mg/min    ______________________________________    propane   98.7         93.6     3600    hydrogen  1            0.043    1.6    triglycerides              0.3          6.3      240    ______________________________________

The triglycerides (tg) were in this case a commercial vegetable oil.

Reaction conditions:

    ______________________________________    catalyst      5% Pd on char coal (E 101 O/D 5%                  Degussa AG    reactor volume                  2.5 ml    reactor time  12 sec    temperature   50° C.    pressure      100 bar    ______________________________________

productivity and product quality:

    ______________________________________    productivity       5 000 kg tg/m.sup.3 h    Iodine-value       reactor inlet = 140                       reactor outlet = 0.1    FA with trans      <0.1% of all FA    ______________________________________

Comments:

This example shows that a high productivity (5000 kg triglycerides/m³ h)can be attained at near-critical conditions. The results above is onlyan example. We do not claim that it is the optimal conditions for theprocess.

We claim:
 1. A process for hydrogenation of a hydrogentable substratecomprising the steps ofmixing the substrate, hydrogen gas and a solventto form a substantially homogeneous solution in a super-critical ornear-critical state; and bringing the substantially homogenous solutioninto contact with a hydrogenation catalyst under conditions of time,temperature and pressure effective to produce hydrogenated substrate asa constituent of the substantially homogeneous solution.
 2. A processaccording to claim 1, wherein the solvent is selected from the groupconsisting of ethane, ethene, propane, propene, butane, butene, CO₂,dimethyl ether, freons, N₂ O, N₂, NH₃ and mixtures thereof.
 3. A processaccording to claim 1, wherein the substrate comprises lipids.
 4. Aprocess according to claim 1, wherein the solvent comprises a saturatedhydrocarbon or an unsaturated hydrocarbon, which results onhydrogenation in a saturated hydrocarbon.
 5. A process according toclaim 2, wherein the solvent is propane.
 6. A process according to claim1, wherein a noble metal or a nickel catalyst is used for the selectivehydrogenation of a substrate containing a carbon-carbon-double bond(C═C).
 7. A process according to claim 1, further comprising the stepsof determining the iodine number during the formation of hydrogenatedsubstrate and interrupting the reaction when the desired iodine numberhas been obtained, the desired iodine number being near zero for fullhydrogenation and above zero for partial hydrogenation.
 8. A processaccording to claim 1, wherein zinc chromite or any other catalytic saltof zinc is used as a catalyst for the selective hydrogenation of asubstrate having the formula COOR to form hydrogenated substrate havingthe formula C--OH and HO--R.
 9. A process according to claim 1, whereincopper chromite, copper free from chrome, or any other catalytic salt ofcopper is used as a catalyst for the selective hydrogenation of asubstrate having the formula COOR to form hydrogenated substrate havingthe formula C--OH and HO--R or the hydrogenation of a substratecontaining carbon-carbon double bonds or for both reactionssimultaneously.
 10. A process according to claim 1, wherein thesubstrate comprises oxygen.
 11. A process according to claim 10, whereinthe solvent is selected from the group consisting of CO₂, N₂, NH₃, andmixtures thereof.
 12. A process according to claim 11, wherein thesolvent is CO₂.
 13. A process according to claim 10, wherein a noblemetal is used as catalyst for the hydrogenation of oxygen to hydrogenperoxide.